RNA viruses, in general, are deadly human pathogens, and highly efficient in evading antivirals and vaccines, due in part to their ability to mutate rapidly. The annual Flu epidemics and the recent emergence of SARS are important reminders. The long-term goal of this project is to understand the major areas of host-virus interaction in the gene expression and signal transduction of negative-strand RNA viruses, using primarily the human respiratory syncytial virus (RSV) as a model. RSV is a severe lung pathogen in children, causing respiratory diseases and asthma, and claiming nearly a million lives globally each year. In the US alone, RSV infection leads to about 100,000 hospitalizations, costing roughly $350 million to the US taxpayers. The immunopathology of RSV also is highly complex, making it difficult to formulate a reliable vaccine or antiviral. We reasoned that a prudent approach to the management of RSV should take into account the host-virus interactive pathways. In the last few years, we have shown that cellular actin is an essential transcription factor for RSV. Our recent studies using phenotypic knockdown of cellular proteins by a relatively novel strategy, known as "RNA interference", have revealed an essential role of 3 cytoskeletal-regulatory proteins (CRPs) in RSV maturation. These proteins are: profilin, VASP, and zyxin. Previous studies demonstrated that these proteins were relatively non-essential for the host cell. Thus, we propose that these CRPs could be potential targets for an antiviral regimen. Moreover, an understanding of their role in RSV morphogenesis would shed light on the fundamental mechanism of how the cytoskeleton may play a critical role in RNA viral maturation. Thus, the Specific Aims of the proposal involve detailed studies of: (i) the role of actin as a viral transcription factor;and (ii) the involvement of the CRPs in viral morphogenesis. The available CRP knockout mice strains will be used to complement and extend these studies to an animal model. Together, these results should lead to a better understanding of the replication of RSV in particular and of RNA viruses in general, and pave the way for a more reliable management of the viral diseases.